In a current communications system, to increase wireless resource utilization and a network capacity of an entire system, a terminal may be handed over among multiple cells. When communication quality of a serving cell becomes increasingly poor, a network may control the serving cell to send a change command to the terminal, so that the terminal is handed over to another cell with the best communication quality in an active set. The active set refers to a set of cells to which a terminal establishes a connection. Data transmission between a user and a network is performed by using a cell in the active set.
However, because the communication quality of the serving cell is already extremely poor, when the serving cell sends the change command to the terminal, the terminal may not receive the change command, which causes a small transmission success rate of the change command. To improve this situation, a better approach at present is to use all cells except the serving cell in the active set as preconfigured cells, and a resource of a cell that serves as a serving cell is configured in advance for the terminal, where the preconfigured resource may include a type of a serving cell change completion message, a transaction identifier used by a serving cell completion message, indication information of whether serving cell change resets a media access control (MAC) layer entity, an identifier, of a user equipment (UE) in a preconfigured cell, configuration information of a preconfigured high-speed downlink shared channel (HS-DSCH) serving cell, and configuration information of an enhanced dedicated channel (E-DCH) serving cell, where the configuration information of the HS-DSCH serving cell refers to information about a resource, such as a channel, used by the UE after the preconfigured cell becomes a serving cell, and the configuration information of the E-DCH serving cell refers to information about a resource, such as a channel, used by the UE after the preconfigured cell becomes a serving cell. Afterwards, cell change is triggered according to an event 1D in intra-frequency measurement control, and when the preconfigured cell triggers the event 1D, the network controls this preconfigured cell to send a change command to the terminal, and the terminal completes a serving cell change process according to the change command. This process is also referred to as “enhanced serving cell change”. For example, in US2011/0014917A1, improved configuration of HS-DSCH serving cell change is disclosed, and in this configuration, when a neighboring cell whose pilot signal strength is stronger than that of a current serving cell is detected (equivalent to triggering the event 1D), a change command is sent to the terminal by using this neighboring cell with stronger pilot signal strength.
In the prior art, only the event 1D is considered when enhanced serving cell change is performed, but a non-event 1D in the intra-frequency measurement control is not considered, and the non-event 1D includes an event 1A, an event 1B, an event 1C, an event 1E, and an event 1F. If the serving cell or another cell triggers the event 1B, 1C, or 1F, there are two problems in the prior art: 1. The network cannot determine whether the terminal needs to perform serving cell change. 2. Even if the network can determine that the terminal needs to perform serving cell change, the network cannot determine cell information of a target cell for the serving cell change, because there may be at least one cell that is stronger than the serving cell in the active set. Therefore, when the non-event 1D is triggered, if the network determines that serving cell change needs to be performed, the network still controls the serving cell to send a change command, which still causes a small transmission success rate of the change command.
A definition of each event in the intra-frequency measurement control is as follows:
Event 1A: Pilot signal strength of a cell that does not belong to the active set increases, and a signal measurement value of a target cell enters a reporting range of relative active set quality.
Event 1B: Pilot signal strength of a cell in the active set reduces, and a signal measurement value of a target cell leaves a reporting range of relative active set quality.
Event 1C: Pilot signal strength of a cell outside the active set is greater than pilot signal strength of the poorest cell in the active set.
Event 1D: Pilot signal strength of a cell (not a serving cell) in the active set is greater than pilot signal strength of a current serving cell.
Event 1E: Pilot signal strength of a cell exceeds an absolute threshold.
Event 1F: Pilot signal strength of a cell is lower than an absolute threshold.